1. Field of the Invention
The present invention relates to a method for transmitting frames in a wireless local area network and data structure for the same, and more particularly, to a method and data structure for a repeater in a wireless local area network to transmit frames according to the IEEE 802.11 protocol.
2. Description of the Related Art
The IEEE 802.11 defines the format of data frame for wireless local area network. FIG. 1 illustrates some important fields of a data frame defined in IEEE 802.11. The data frame includes four address fields for recording basic service set identifier (BSSID), source address (SA), destination address (DA), transmitter address (TA) and receiver address (RA).
The destination address can be a unique address or a broadcast address, which is the destination of the frame. The source address is the address of the station, which generates the frame. The transmitter address is the address of the station, which transmits the frame in wireless medium, and the transmitter is connected to an access point (AP) in a wireless distribution system. The receiver address is the address of the next station, which will receive the frame, and the receiver also connects to the access point in the wireless distribution system.
The access point can be a bridge or a repeater. The bridge is used to connect the wireless local area network and the local area network such as ether network for sharing the Internet source. The repeater transmits signal in a circuitous manner to overcome the obstacle of the building so as to elongate the communication distance. Each station decides whether to receive a frame according to the content of the address 1 field. A station will receive the frame if the content of the address 1 is the same as the address of the station itself, otherwise it will discard the frame. The receiver can transmit an acknowledgement frame to the address recorded in the address 2 field if necessary.
FIG. 2A illustrates some important fields of a data frame 10 transmitted from a source station to a repeater, and FIG. 2B illustrates some important fields of a data frame 12 forwarded to a bridge by the repeater. As shown in FIG. 2A and FIG. 2B, the repeater must transform the data frame 10 into data frame 12 before forwarding to the bridge. The logic value of the “To DS” field is set to 1 for indicating that the data frame 12 is transmitted to an access point (the bridge) of a distribution system, and the logic value of the “From DS” field is set to 1 for indicating that the data frame 12 is transmitted from an access point (the repeater). The address 1 field records the receiver address (the address of the bridge), the address 2 field records the transmitter address (the address of the repeater), the address 3 field records the destination address and the address 4 field records the source address.
After receiving the data frame 12, the bridge will transmit an acknowledgement frame to the repeater according the address recorded in the address 2 field of the data frame 12, and the repeater will transmit an acknowledgement frame to the source station according the address recorded in the address 2 field of the data frame 10. To transform the data frame 10 into data frame 12, the repeater must change the content of the “From DS” field, the address 1 field, the address 2 field, the address 3 field and the address 4 field. Additionally, the above-mentioned method is inconvenient to design and increases the cost, since the data frame 12, transmitted from the repeater to the bridge, completely uses 4 address fields to store the bridge address, the repeater address, the destination address and the source address, respectively.
The bridge must identify the type of the repeater before receiving data frame from or transmitting to the repeater. However, the repeater and the bridge made by different companies might use proprietary protocol to transmit or receive frames that increase the complexity for setting a bridge which does not conform to requirement of the market.